The invention is directed to multilayer thin film coatings which can substantially reduce the surface reflectivity of materials, particularly materials with a high index of refraction, over a broad range in the infrared spectrum.
Infrared transmitting optical materials are finding wide application in various laser, pyrometer and analyzer systems. The infrared spectral range with wavelengths between approximately 1.7 .mu.m and 10.0 .mu.m is particularly useful for analyzer applications because nearly all organic materials and products of combustion demonstrate unique infrared absorption bands in this wavelength interval. One such analyzer system utilizes an acousto-optic tunable filter which operates through the interaction of high frequency acoustic waves with light waves in a suitable crystal. Infrared acousto-optic tunable filters can have a light transmission loss of more than 50 percent at the crystal's surface due to the high index of refraction of the crystal. The transmission loss reduces the detector signal-to-noise ratio achievable in acousto-optic systems. The use of additional transmitting components, such as polarizers, which are often required in infrared analyzer systems, contributes additional surface reflection with resulting transmission loss.
It is an object of this invention to provide a multilayer thin film antireflection coating which substantially reduces the surface reflectivity of infrared transmitting materials, particularly materials with a high index of refraction.
It is also an object of this invention to provide an infrared transmissive device having significantly improved transmission characteristics due to reduced surface reflectivity.
It is still another object of this invention to provide a wire grid polarizer adapted for use with an infrared transmissive device. The wire grid polarizer includes a multilayer thin film antireflection coating which improves the polarizer's infrared transmission characteristics.